Periodontal ligament.pptx by Dr. Ira Gupta

Periodontal ligament is a supporting tissue of the teeth and a major component of the periodontium

1. Periodontal ligament 1

2. CONTENTS Introduction Development Cells of PDL Extracellular substance: Fibers Collagen Ground substance Structures present in connective tissue: Blood vessels Venous drainage Lymphatic drainage Nerves Cementicles Functions Age changes in periodontal ligament Unique features of periodontal ligament Clinical considerations 2

3. INTRODUCTION The periodontal ligament is the soft, rich vascular and cellular connective tissue which surrounds the roots of the teeth and joins the root cementum with the socket wall. (LINDHE) The periodontal ligament, in coronal direction, is continuous with the lamina propria of gingiva and is demarcated from the gingiva by the collagen fiber bundles(alveolar crest fibers) 3

4. Other terms used for PDL were:- Desmodont , Gomphosis , Pericementum , Dental periosteum , Alveolodental ligament Periodontal membrane. PDL Width of large no. ranges from0.15 to 0.38 mm*. Thickness :-0.21 mm in young adult, 0.18mm in mature adult, and 0.15 mm in older adult. Hour glass appearance.* PDL appears as a radiolucent area between radiopaque lamina dura of alveolar bone proper and cementum. PDL space :-0.4 to 1.5mm on radiograph. 4

5. DEVELOPMENT Shortly after the beginning of root formation and the formation of the outer dentinal layer of root, the PDL is formed. The external and internal dental epithelia proliferates from cervical loop of dental organ to form double layered Hertwig’s epithelial root sheath between the dental papilla and dental follicle or sac. PDL is derived from dental follicle. The cells of dental follicle divide and differentiate into fibroblasts ,cementoblasts and osteoblasts. 5

6. The fibroblast synthesize the fibers and ground substance of PDL. These fibers of PDL get embedded at one end into the newly formed cementum laid by cementoblasts and at other end into the bone laid by osteoblasts. 6

7. DEVELOPMENT OF PDL FIBERS 7

8. CELLS OF PDL The cells of the PDL may be divided into 3 main categories: SYNTHETIC CELLS Cementoblasts Fibroblasts Osteoblasts RESORPTIVE CELLS Osteoclast Fibroblasts Cementoclasts PROGENITOR CELLS EPITHELIAL RESTS OF MALASSEZ DEFENSE CELLS Mast Cells Macrophages Eosinophils 8

9. SYNTHETIC CELLS FIBROBLASTS Fibroblasts are the most common cells in periodontal ligament. They constitute about 65% of total population. They appear as ovoid or elongated cells with pseudopodia like process. FUNCTION: Production of various types of fibers & is also instrumental in the synthesis of connective tissue matrix. The fibroblast is stellate shaped cell which produces: 1. COLLAGEN FIBERS 2. RETICULIN FIBERS 3. OXYTALAN FIBERS 9

10. Various stages in the production of collagen fibers are as follows: The first molecule released by fibroblasts is tropocollagen which contains three polypeptide chains intertwined to form helix. Tropocollagen molecules are aggregated longitudinally to form protofibrils , which are subsequently laterally arranged parallel to form collagen fibrils. Importantly in inflammatory situations such as those associated with periodontal diseases, an increased expression of matrix metalloproteinase's occurs that aggressively destroys collagen. Thus attractive therapies for controlling tissue destruction may include host-modulators that have the capacity to inhibit metalloproteinase's. 10

11. OSTEOBLAST Osteoblasts are derived from the multipotent mesenchymal cells. They cover the periodontal surface of the alveolar bone. These are the modified endosteum . The surface of the bone is largely covered by osteoblasts in various stages of differentiation as well as occasional osteoclasts . 11 CEMENTOBLASTS These cells line the surface of cementum, but are not regularly arranged as Osteoblasts. Prominent cytoplasmic processes are present in the cementoblasts depositing cellular cementum and absent in cementoblasts depositing acellular cementum.

12. 2. RESORPTIVE CELLS A)OSTEOCLASTS – Resorb bone. The surface of an osteoclasts which is in contact with bone has a ruffled border. Resorption occurs in two stages: The mineral is removed at bone margins and then exposed organic matrix disintegrates . The osteoclasts demineralise the inorganic part as well as disintegrates the organic matrix .   B)CEMENTOCLASTS – Cementoclasts are found in periodontal ligament but not remodeled like alveolar bone and periodontal ligament. These are found on the surface of cementum.   C)FIBROBLASTS – Fibroblasts are capable of both synthesis and resorption. They exhibit lysosomes , which contain collagen fragments undergoing digestion. The presence of collagen resorbing fibroblasts in a normal functioning periodontal ligament indicates resorption of fibers occurring during remodeling of periodontal ligament. 12

13. PROGENITOR CELLS – Progenitor cells are the undifferentiated mesenchymal cells, which have the capacity to undergo mitotic division and replace the differentiated cells dying at the end of their life span. When cell division occurs, one of the daughter cells differentiate into functional type of connective tissue cells. The other remaining cells retain their capacity to divide. EPITHELIAL CELL RESTS OF MALASSEZ- These cells are the remnants of the epithelium of Hertwig’s Epithelial Root Sheath and are found close to cementum. These cells exhibit monofilaments and are attached to each other by desmosomes . The epithelia cells are isolated from connective tissue by a basal lamina. 13

14. DEFENCE CELLS A) MAST CELLS- The granules contain heparin and histamine. The release of histamine into the extracellular compartment causes proliferation of the endothelial and mesenchymal cells. Degranulate in response to antigen- antibody formation on their surface. B) MACROPHAGES – Macrophages are derived from blood monocytes and are present near the blood vessels. Macrophages help in phagocytosing dead cells and secreting growth factor, which help to regulate the proliferation of adjacent fibroblasts. C] EOSINOPHILS- Occasionaly seen in PDL. The cells are capable of phagocytosis . 14

15. EXTRACELLULAR SUBSTANCES FIBERS Collagen Elastic Reticular Secondary Indifferent fiber plexus GROUND SUBSTANCE Proteoglycans Glycoprotein 15

16. COLLAGEN The connective tissue matrix is composed of several organic constituents including collagens, noncollagenous proteins and proteoglycans. Among these the collagens are the principal structural components. TROPOCOLLAGEN MOLECULES COLLAGEN FIBRILS (Collagen fibrils have a transverse striation with a characteristic periodicity of 64 nm. Small mean diameter of 45-55nm) COLLAGEN BUNDLES (The collagen is gathered to form bundles approx. 5µm in diameter. These bundles are termed as principal fibers ) 16

17. Two main types of collagen in PDL: Type I collagen (70%of PDL) uniformly distributed in the pdl. Type III collagen (20% of PDL). It is covalently linked to type I collagen through out the tissue. It is found in periphery of sharpey’s fiber attachment into alveolar bone. Function- Involved with collagen turnover, tooth mobility and collagen fibril diameter. Small amount of type V and VI collagen and traces of type IV and VII collagen are present in PDL. Type VI –ramifies the extracellular matrix and also maintain its integrity and elasticity. Type IV AND VII are associated with epithelial cell rests and blood vessels. Type XIII collagen believed to occur with in the PDL , only when the ligament is fully functional. 17

18. PRINCIPAL FIBERS Transseptal group : extend interproximally over alveolar crest and embedded in cementum of adjacent teeth. Alveolar crest group: extend obliquely from cementum just beneath JE to alveolar crest. prevent extrusion and resist lateral tooth movements. Horizontal group: extend at right angles to tooth from cementum to alveolar bone. Oblique group: largest group extend from cementum in a coronal direction obliquely to bone. They bear brunt of vertical masticatory stresses . Apical group: radiate from cementum to bone at apical region of socket. lnterradicular fibers: fan out from cementum to tooth in furcation areas of multirooted teeth . 18

19. FIBERS FUNCTIONS ALVEOLAR CREST Retain tooth in socket; oppose lateral forces; protect deeper periodontal ligament structures. HORIZONTAL Restrain lateral tooth movement. OBLIQUE Resist axially directed forces. APICAL Prevent tooth tipping; resist luxation ; protect blood, lymph , nerve supplies to tooth. INTER-RADICULAR Resist tipping, torquing & luxation. 19

20. SHARPEY’S FIBERS Collagen fibers are imbedded into cementum on one side of the periodontal space and into alveolar bone on the other. The embedded fibers are termed as sharpey’s fibers. These fibers are more numerous but smaller at their attachment into the cementum than alveolar bone. Few sharpey’s fibers passes uninterruptedly through the bone of the alveolar process, these fibers are termed as transalveolar fibers. Sharpey’s fibers calcify to a certain degree and are associated with an abundance of noncollagenous proteins namely , osteopontin and bone sialoproteins. 20

21. OXYTALAN FIBERS Apico -occlusal orientation. Bundles of microfibrils . Parallel to root surface. Regulate vascular flow. 21 ELUNIN FIBERS Seen as bundles of microfibrils embedded in a relatively small amount of amorphous elastin . It consist of a microfibrillar component surrounding an amorphous core of elastin protein. The microfibrillar component is located around the periphery and scattered through out the amorphous component These fibers are observed only in the walls of afferent blood vessels .

22. RETICULAR FIBERS Fine immature collagen fibers. Argyrophilic staining properties. Related to basement membrane of blood vessels and epithelial cells which lies with in the PDL. SECONDARY FIBERS Located between and among the principal fibers . Represents newly formed collagenous elements . Non-directional and randomly oriented . Associated with paths of vasculature and nervous elements . INDIFFERENT FIBER PLEXUS These small collagen fibers run in all direction forming a plexus. Some author consider it to be an artifact produced by preparation. INTERMEDIATE PLEXUS Under light microscope, it is seen that some fibers arises from cementum and bone are joined in the mid region of the periodontal space. This give rise to a distinct zone called as intermediate plexus. The remodeling of fibers takes place in this region. 22

23. GROUND SUBSTANCE Ground substance is a gel like matrix and consist of hayaluronate , glycoprotein, proteoglycans, glycosaminoglycans and substrate adhesion molecules. 65% of the volume in the PDL. Comprises : 70% water Glycosaminoglycans ( Hexosamine , Heparin sulfate and Hexuronic acid.) Glycoproteins ( Fibronectin and Laminin .) Proteoglycans ( Chondroitin sulfate and Dermatan sulfate) Substrate adhesion molecules ( Tenascin , Osteonectin , Laminin , Undulin And Fibronectin) Function : Exchange of metabolites between microcirculation and cells. Enables tooth to withstand stress along with fibers. PDL contains a glycoprotein “fibronectin” occurs in filamentous form. It contains chemical groups that attach to the surface of the fibroblasts, collagen, proteoglycans and fibrin. Proteoglycans play a role in transmitting pressure and protect periodontal ligament from damage. 23

24. STRUCTURES PRESENT IN CONNECTIVE TISSUE: Blood vessels: Inferior and superior alveolar arteries to the mandible and maxilla and reaches the PDL from 3 sources : Branches from apical vessels that supply dental pulp. Branches from intra-alveolar vessels that penetrate the alveolar bone horizontally to enter periodontal ligament. Branches of gingival vessels. They enter periodontal ligament from coronal direction. 24

25. The arterioles in PDL ranges from a diameter of 15-50µm(avg. 20µm). The PDL has some specialized feature in the vasculature namely, the presence of large no. of fenestrations in the capillaries and a cervical plexus of capillary loops. These features possibly might be related to the high metabolic requirement of PDL because of rate of turn over. Incisor<molar. Middle 3 rd <apical 3 rd <cervical 3 rd (in single rooted tooth). Due to functional Middle 3 rd= apical 3 rd <cervical 3 rd (in multi rooted tooth). variations at different sites. Venous drainage Accompany their arterial counterparts. Larger in diameter with mean average of 28µm. These channels receives blood from the capillary network and also specialized stunts called glomera in the PDL. In some parts of PDL, particularly around the apex a dense venous network is generally seen. 25

26. LYMPHATIC DRAINAGE: A network of lymphatic vessels follow the path of blood vessels. The flow is from the ligament towards and into the adjacent alveolar bone. The flow is via alveolar lymph channels which are joined by the dental and lnterradicular lymph channels . NERVES PDL has functionally 2 types of fibers:- large fibers( myelinated ) Nerve fibers small fibers( myelinated or unmyelinated ) Unmyelinated small fibers are associated with blood vessels and presumably are autonomic. 26 SENSORY AUTONOMIC Associated with nociception and mechanoception , with pain, touch, pressure and proprioceptive sensation. Associated with blood vessels.

27. CEMENTICLES Cementicles are small, spherical particles of cementum that form during development. The origin of these calcified bodies is not established but it is possible that degenerated epithelial cells form the nidus for their calcification. They are of two types; the free cementicles which lie free in the periodontal ligament and the sessile or attached cementicles which are attached to the cementum surface or  incorporated into the cementum layer as imbedded cementicles. 27

28. FUNCTIONS PHYSICAL : Soft tissue “casing” – vessels & nerves. Transmission of occlusal forces to the bone. Attachment of the teeth to the bone. Maintenance of the gingival tissues in proper relationship to the teeth. Resistance to the impact of occlusal forces ( shock absorption). 28

29. RESISTANCE TO THE IMPACT OF OCCLUSAL FORCE ( SHOCK ABSORPTION) TENSIONAL THEORY VISCOELASTIC SYSTEM THEORY States that the principal fibers of the PDL are the major factor in supporting the tooth and transmitting forces to the tooth. 29 States that the displacement of the tooth is largely controlled by fluid movements, with fibers having a secondary role .

30. TRANSMISSION OF OCCLUSAL FORCES TO BONE : Arrangement of PDL is similar to a Suspension bridge or a hammock . Axial force - root displacement into alveolus. - oblique fiber alter their wavy and untensed pattern ;assume their full length ;& sustain major part of axial force. Horizontal / Tipping force – 1. within confines of periodontal ligament. 2. facial & lingual bony plate displacement. 30 Distribution of faciolingual forces  (arrows)  around the axis of rotation  (R)  in a mandibular premolar. The periodontal ligament fibers are compressed in areas of pressure  (P)  and taut in areas of tension  (T)

31. FORMATIVE & REMODELING: Cells in PDL – formation & resorption of cementum & bone. PDL cells responds directly to mechanical forces – activation of mechanosensory signaling system ( adenylate cyclase, stretch - activated ion channels & changes in cytoskeleton organization). Constant remodeling. Fibroblast form collagen & residual mesenchymal cells – osteoblasts & cementoblasts. A rapid turnover of sulfated glycosaminoglycans in the cells and amorphous ground substance of PDL also occurs. 31

32. NUTRITIONAL & SENSORY: PDL provide nutrients to cementum, bone and gingiva by way of the blood vessels& lymphatic drainage. Sensory nerve fibers – tactile, pressure & pain. Nerves follow course of blood vessels . 1- Free endings – tree like 2- Ruffini’s Corpuscles – apical area. 3- Tactile ( Meissner’s ) corpuscles – midroot region. 4- Spindle type nerve endings – pressure & vibration; apical area. 32 Free endings

33. AGING OF PDL The number of cells and their activity decrease, scalloping occurs in cementum and alveolar bone. Some fibers are attached at the peak of those scallops only and not in the depressions. this adversely effect the support to the teeth. The activity of cells and their number decreases with age. With aging due to restricted and soft diet physiological stimulation to the PDL is reduced. Vasuclarity Cellularity Thickness Cementicles. Decreased organic matrix production. Increased elastic fibers. 33

34. CLINICAL CONSIDERATION Trauma to the ligament results in resorption of bone and ligament is widened, so the teeth become loose. If the trauma is eliminated, repair will take place. Resorption and formation of both bone and PDL play an important role in the orthodontic tooth movement. Inflammation of the pulp reaches to the apical PDL and replaces its fiber bundles with granulation tissue, which is called as granuloma . 34

35. Granuloma further progresses into apical cyst(most common pathological lesion of jaws). Teeth are slightly more mobile in the early morning then in the evening. Non functional teeth – thin Excessive occlusal stress. Age . 35

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